|Langusch, J; Matzner, E: Long-term modelling of nitrogen turnover and critical loads in a forested catchment using the INCA model, Hydrology and Earth System Sciences, 6, 395-402 (2002)|
Many forest ecosystems in Central Europe have reached the status of N saturation due to chronically high N deposition. In consequence the NO3 leaching into ground- and surface waters often is substantial. Critical loads have been defined to abate the negative consequences of the NO3 leaching such as soil acidification and nutrient losses. Today, the steady state mass balance method is often used to calculate critical loads for N deposition in forest ecosystems. The aim of this study was to test the suitability of the dynamic model INCA (Integrated Nitrogen Model for European Catchments) to simulate long-term effects of changing N deposition and to assess critical loads for N for the Lehstenbach catchment (Fichtelgebirge, NE Bavaria, Germany) under different hydrological conditions. The site is stocked with Norway spruce (Picea abies (L.) Karst.) of different age. The actual mean annual mineral N flux with throughfall at this site is about 21 kg ha-1 with 1100 mm precipitation. INCA was calibrated for the period 1995 - 1999. Climatical data of 7 years were replicated to get a 100 year time scale. A concentration of 0.4 mg N L-1 in runoff was defined as threshold value for the calculation of critical loads. Long-term scenarios of increasing and decreasing N deposition indicated that under the conditions at the Fichtelgebirge the response of nitrate concentrations in runoff to changing N deposition is buffered by the large groundwater reservoir. The critical load with respect to nitrate in runoff (0.4 mg L-1 as threshold value) simulated by the INCA model was 9.7 kg N ha-1 a-1. Under conditions of lower precipitation (520 mm) the resulting critical load was 7.7 kg N ha-1 a-1, suggesting the need to account for different hydrological conditions when calculating critical loads. The INCA model seems to be suitable to calculate critical loads for N in forested catchments under varying hydrological conditions e.g. as a consequence of climate change.